Method For Measuring Chroma Value By a Colorimeter

ABSTRACT

A method for measuring chroma value by colorimeter to solve the drawbacks of conventional technologies, such as an inaccurate illuminant and the filter of color-matching function is difficult to be deposited and manufactured within an filter mod colorimeter, and an expensive spectrometer used within an spectrum mode calorimeter. The present invention does not need the spectrometer and the filter of color-matching function, and can measure an accurate chroma value of an object by using a multi-band illuminant illuminating the object and a power meter. Besides, the multi-band illuminant can be adjusted the illumination condition of standard illuminator under different color temperature, and measure the chroma value of the object under different color temperature. The accuracy of the measured chroma value is up to the level of the spectrum mode colorimeter, and the price is cheaper than the spectrum mode calorimeter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for measuring the chroma valueby a colorimeter, and more particularly to a measuring method that canget the accuracy level of the measured chroma value up to the spectrummode calorimeter but does not need to use the filter of color-matchingfunction that is difficult to be deposited and manufactured and ischeaper than the spectrum mode colorimeter.

2. Description of Related Art

A colorimeter is used to measure the data of color performance of anobject in different appropriate standard lighting environments. Thecolorimeter can objectively measure the color of different objects, forexample, the reflective surface of plastics, paint, coating, printingetc., for achieving the control, duplication and delivery of colorseffectively. Therefore, the colorimeter is one of the importantinstruments regardless of the industrial application or the academicresearch.

In order to quantify and define color by a scientific way, CommissionInternational del'Eclairage (CIE) established a color-matching functionx(λ), y(λ) and z(λ) under equal energy condition in 1931. The appearedcolor of any illuminated object, such as the spectral intensity of anilluminant S(λ), the reflectance of the object R(λ), can be calculatedby the color-matching function based on XYZ color basis. The XYZ colorspace is named CIE 1931 color space system. It is inconvenient onanalysis and application to depict color coordinate on three-dimensionalcoordinate as getting a group of XYZ color coordinate data andconsidering the position in coordinate space. Based on the concept ofthe luminance normalization, the equation of an xy color coordinate isfirst defined as x+y+z=1. while dealing with XYZ color coordinate,wherein the color space defined by xy is named CIE xy chromaticitydiagram.

Nowadays, the measurement of the chroma value by reflection modecolorimeter is according to the standard CIE method to compute the totalenergy by the reflective light of the object, the CIE color-matchingfunction and a weighting consideration on different wavelengths. Theindividual chroma value depended on the computed total energy and thedifferent color-matching function is obtained.

The foregoing procedure, such as the weighting of color-matchingfunction and the summation of the stimulus energy, can be generalizedand divided into two classifications at the design principle

A. Filter Mode Colorimeter:

Referring to FIG. 7, the filter mode calorimeter need to cooperate witha specific standard illuminant 20, such as CIE standard illuminant A,CIE standard illuminant C, CIE standard illuminant D etc., and thespecific standard illuminant 20 illuminates on the surface of an object21. A reflective light 22 that reflects from the surface of the object21 passes through a filter of color-match function 23 and is receivedseparately by a multi-band power meter 24. The chroma value of object 21is got afterward.

However, the marketed standard illuminant D is not accurate enough andthe filter of color-matching function 23 is difficult to be depositedand manufactured, the measured chroma value is not easy to get theaccurate level.

B. Spectrum Mode Calorimeter:

Referring to FIG. 8, an object 31 is illuminated by a known white lightilluminant 30, and a reflective light 32 that reflects form the surfaceof the object 31 is received and the reflection index of the object 31is computed by a spectrometer 33 in a calorimeter. The chroma value ofthe object 31 illuminated on the different standard illuminants will befigured out through the calculation of the calorimeter.

However, the spectrum mode calorimeter is more expensive even though themore accurate chroma value of the object can be computed by spectrummode calorimeter.

There are some drawbacks in the conventional technologies. Such that themeasured chroma value by the filter mode colorimeter that is equippedthe marketed standard illuminant D is not accurate enough. Besides, thefilter of color-matching function used to receive the reflective lightis difficult to be deposited and manufactured and is inconvenient formass production.

In addition, the more accurate chroma value is got through thereflective light received by the spectrometer in the spectrum modecalorimeter. However, the spectrometer is more expensive and notagreeable to the consideration of the economic benefits.

Due to the drawbacks of the conventional colorimeters, the inventortakes the investigation and the research for solving the problems of thecolorimeter based on the experiences of research and manufacture in theindustrial field. Finally, the inventor creates a method for measuringthe chroma value by a calorimeter and to exactly improve theabove-mentioned drawbacks.

SUMMARY OF THE INVENTION

The main objective of the present invention is to provide a method forachieving the accuracy of the measured chroma value is up to the levelof the spectrum mode colorimeter and is cheaper than the spectrum modecalorimeter.

To achieve the objective, the present invention provides a method formeasuring the chroma value by a calorimeter, comprising the steps of:

(a) illuminating on the surface of an object with a multi-bandilluminant;

(b) forming a reflective light 13 which reflect form an illuminatinglight 12 on the surface of the object 11, and wherein the reflectivelight 13 passes through a power meter 14 within the calorimeter;

(c) computing a chroma value of the object by the luminous intensitythat is received by the power meter.

Therefore, the present invention is easy to adjust color temperature bythe multi-band illuminant. Compared with the conventional filter modecalorimeter using the standard illuminant D, it can get the chroma valueup to the accuracy level of the spectrum mode colorimeter and receivethe reflective light by the power meter to avoid the disadvantage ofusing the expensive spectrometer.

The present invention provides a method to measure the chroma value by acalorimeter, and to achieve the accurate chroma value similar to thespectrum mode colorimeter by illuminating the object by the multi-bandilluminant. Furthermore, It is cheaper than the spectrum modecalorimeter and improves the drawbacks of the filter mode colorimeterand spectrum mode calorimeter.

Further benefits and advantages of the present invention will becomeapparent after a careful reading of the detailed description withappropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of a method of the present invention.

FIG. 2 is a schematic diagram of a method of the present invention.

FIG. 3 is a chroma value of an illuminant D65 illuminating on an objectof the present invention.

FIG. 4 is a coordinate diagram of a frequency response of light power.

FIG. 5 is a coordinate diagram of a simulation result of using 24 piecesof LED.

FIG. 6A is a simulation result of CIE standard illuminant A.

FIG. 6B is a simulation result of CIE standard illuminant C.

FIG. 7 is a conventional filter mode colorimeter.

FIG. 8 is a conventional spectrum mode colorimeter.

DETAILED DESCRIPTION OF THE INVENTION

At first please referring to FIG. 1 and FIG. 2, the present inventionprovides a method for measuring the chroma value by a colorimeter,comprising the steps of:

(a) illuminating on the surface of an object 11 with a multi-bandilluminant 10;

The multi-band illuminant 10 can individually make a plurality ofdifferent spectrum illuminants, such as S(λ)*x(λ), S(λ)*y(λ) andS(λ)*z(λ) by adjusting a CIE standard illuminant under different colortemperature. And the multi-band illuminant 10 comprises a plurality ofsingle wavelength lights which is distributed in the visible light band,such as a demanded spectrum illuminant of the calorimeter arbitrarilycomprises plural pieces of color light emitting diode (LED) wherein theamount of color LED can be 24 pieces. The multi-band illuminant 10 has aplurality of illumination tubes that each illumination tube has a cover,and plural layers of phosphor with different colors are coated on theinner side of each cover, for example the red phosphor, the greenphosphor and the blue phosphor etc., and a LED is disposed within thecover of an illumination tube to excite the phosphor. The multi-bandilluminant will be acquired by adjusting the spectrum illuminants of theplurality of illumination tubes, wherein the LED is prefer to use theultraviolet LED (UV LED).

(b) forming a reflective light 13 which reflect form an illuminatinglight 12 on the surface of the object 11, and wherein the reflectivelight 13 passes through a power meter 14 within the colorimeter;

(c) computing a chroma value of the object by the luminous intensitythat is received by the power meter;

Referring to FIG. 3, it shows the chroma value of object as anilluminant D65 (6504 K) illuminating on the object. To compute theproduct of the illuminant spectrum S(λ) (D65 spectrum distribution), thereflectance of the object R(λ) and CIE 1931 color-matching function,x(λ), y(λ) and z(λ) individually, and then X, Y; Z data can be obtainedthrough integrating the product between the visible light band (λ=380nm˜830 nm).

The distributed spectrum illuminant, S(λ)*x(λ), S(λ)*y(λ) and S(λ)*z(λ),from the multi-band illuminant illuminates on the object in turn, and tobe received by the multi-band power meter after times the reflectance ofthe object R(λ), that is the same as integration. The X, Y, Z data willbe obtained therefore.

Owing to considering a frequency response of the power meter on everywavelength, the multi-band illuminant is used for forming thedistributed spectrum illuminant individually, such as S(λ)*x(λ)/PM(λ),S(λ)*y(λ)/PM(λ) and S(λ)*z(λ)/PM(λ),

And then,

$X = {k{\int{\frac{{S(\lambda)}{\overset{\_}{x}(\lambda)}}{{PM}(\lambda)}{R(\lambda)}{{PM}(\lambda)}{\lambda}}}}$$Y = {k{\int{\frac{{S(\lambda)}{\overset{\_}{y}(\lambda)}}{{PM}(\lambda)}{R(\lambda)}{{PM}(\lambda)}{\lambda}}}}$$Z = {k{\int{\frac{{S(\lambda)}{\overset{\_}{z}(\lambda)}}{{PM}(\lambda)}{R(\lambda)}{{PM}(\lambda)}{\lambda}}}}$

That is the core of the present invention.

The distributed spectrum illuminant is verified with simulations, asbelow:

As showing in FIG. 4, the multi-band illuminant produces the distributedspectrum illuminant, D65x(λ)/PM(λ), D65y(λ)/PM(λ) and D65*z(λ)/PM(λ), byadopting the frequency response PM(λ) of light power.

Referring to FIG. 5, the light source of the multi-band illuminant issimulated to comprise 24 pieces of LED, and the spectrum distribution isbetween 380 nm and 730 nm.

Referring to FIG. 6A and FIG. 6B, that are the simulation resultsdepended on the CIE standard illuminant A and the CIE standardilluminant C, and the simulated spectral distributions are very close tothe theoretical spectral distribution.

The present invention provides a remixed illuminator as the illuminatorof colorimeter through assembled multi-band illuminants. The remixedilluminator can be adjusted directly to achieve the effect that is liketo the filter of color-matching function. Besides, The present inventiondoes not need the spectrometer and the filter of color-matchingfunction, and can measure an accurate chroma value of an object by usinga multi-band illuminant illuminating the object and a power meter. Theaccuracy of the measured chroma value is up to the level of the spectrummode colorimeter, and the price is cheaper than the spectrum modecalorimeter.

Moreover, the multi-band illuminant can be adjusted the illuminationcondition of standard illuminator under different color temperature andcan directly measure the chroma value on the real condition, that is notlike the result of current status to be obtained through analogizing andcalibrating for different band of illuminants after illuminating andmeasuring by single-band illuminant.

Although the invention has been explained in relation to its preferredembodiment, it is to be understood that many other possiblemodifications and variations can be made without departing from thespirit and scope of the invention as hereinafter claimed.

1. A method for measuring chroma value by a calorimeter, comprising thesteps of: (a) illuminating on the surface of an object with a multi-bandilluminant, and wherein the multi-band illuminant comprises a pluralityof single wavelength lights which is distributed in the visible lightband and the multi-band illuminant individually make a plurality ofdifferent spectrum illuminants, S(λ)*x(λ), S(λ)*y(λ) and S(λ)*z(λ); (b)forming a reflective light which reflect form an illuminating light onthe surface of the object, and wherein the reflective light passesthrough a power meter within the colorimeter; (c) computing an chromavalue of the object by the luminous intensity which is received by thepower meter, wherein the distributed spectrum illuminants, S(λ)*x(λ),S(λ)*y(λ) and S(λ)*z(λ), from the multi-band illuminant illuminate onthe object in turn, and to be received by the multi-band power meterafter times the reflectance of the object R(λ), that is the same asintegration, then the X, Y, Z data are obtained, and owing toconsidering a frequency response of the power meter on every wavelength,multi-band illuminant is used for forming the distributed spectrumilluminants individually, S(λ)*x(λ)/PM(λ), S(λ)*y(λ)/PM(λ) andS(λ)*z(λ)/PM(λ), that is$X = {k{\int{\frac{{S(\lambda)}{\overset{\_}{x}(\lambda)}}{{PM}(\lambda)}{R(\lambda)}{{PM}(\lambda)}{\lambda}}}}$$Y = {k{\int{\frac{{S(\lambda)}{\overset{\_}{y}(\lambda)}}{{PM}(\lambda)}{R(\lambda)}{{PM}(\lambda)}{\lambda}}}}$$Z = {k{\int{\frac{{S(\lambda)}{\overset{\_}{z}(\lambda)}}{{PM}(\lambda)}{R(\lambda)}{{PM}(\lambda)}{{\lambda}.}}}}$2. The method as claimed in claim 1, wherein the multi-band illuminantarbitrarily comprises plural pieces of color light emitting diode (LED)to form a demanded spectrum illuminant of the calorimeter, and candirectly measure the chroma value under different color temperature. 3.The method as claimed in claim 1, wherein the multi-band illuminant hasa plurality of illumination tubes that each illumination tube has acover and the inner of each cover is coated with a different color ofphosphor, and a LED is disposed within the cover of an illumination tubeto excite the phosphor, to adjust the spectrum illuminants of theplurality of illumination tubes for acquiring the demanded multi-bandilluminant.
 4. The method as claimed in claim 3, wherein the LED is anultraviolet LED (UV LED).
 5. The method as claimed in claim 3, whereinthe phosphor is one of a red phosphor, a green phosphor and a bluephosphor.
 6. The method as claimed in claim 1, wherein the amount ofcolor LED is 24 pieces.